A computer fault is believed to be the reason all lines were suspended.

The train network is now up and running but Metro Trains has advised commuters to find alternative transport and says to allow "extra travel time as we restore the timetable or defer travel where possible."

It also announced that "crowd control measures are in place at Southern Cross and City Loop stations" and "to please allow extra time to enter and follow directions from staff."

Uber prices have sky rocketed with surges topping 3.7x the base rate. Yarra Trams has also said massive delays have hit the tram network due to the train fault.

Metro Trains have said their technicians are currently working through the fault but have not said when the network will be up and running.